1. Photoaffinity labeling of rat liver nuclear extracts with 125I-T4 or T3 in the presence and absence of 1000-, 100- and 15-fold molar excess of unlabeled homrones revealed that proteins of molecular weight of 56 and 45 kDa have high affinity for thyroid hormones. Proteolytic digestion of these to covalently labeled proteins showed that they are structurally related. 2. Prepared cDNA probe for rat liver malic enzyme was used to directly demonstrate the increase of malic enzyme mRNA concentration in cytoplasm after T3 treatment.